Light-sensitive image-forming materials useful for applications such as proof paper, print-out paper, overlay films, and the like have widely been used in various photographic applications in which imagewise exposure and development provides an image in the photosensitive portion, namely free-radical photography.
For such applications, particularly useful are materials based on the oxidative color development of a leuco dye by a change into a corresponding dye using a photo-oxidizing agent.
Such materials, which are sensitive to light, may develop color when exposed to regular room light, sunlight or white light even after a dye image has already been formed by light exposure. Such light image-forming materials are therefore not readily handleable.
Various methods has been proposed for preventing color development at the photosensitive portions which have not been exposed at a preceding imagewise exposure step to thereby retain the image thus formed including a method of applying a solution of a reducing agent such as a radical scavenger onto an image-carrying medium by spraying or immersion to retain the original image; a method of forming an image by UV light and then fixing the image by activating a photo-reducing substance by visible light as described in JP-A 47-12879 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") corresponding to U.S. Pat. No. 3,658,543; and a method of incorporating a reducible heat-fixing agent in the photosensitive layer or coating the agent onto the layer, and fixing by heating after the imagewise exposure as disclosed in JP-B 43-29407 (The term "JP-B" as used herein means an "examined Japanese patent publication".).
Among the leuco dyes employed in light image-forming materials, xanthene compounds which develop a black color tone are known having an anilino group at the 2-position, an alkyl group at the 3-position, and a substituted amino group at the 6-position, as described in JP-A Sho-61-137876 corresponding to U.S. Pat. No. 4,749,796.
Such compounds, however, disadvantageously do not develop sufficient color density, and are therefore not satisfactory.